U.S. patent application number 16/522118 was filed with the patent office on 2020-03-19 for control method of a generator.
This patent application is currently assigned to Schneider Electric Industries SAS. The applicant listed for this patent is Schneider Electric Industries SAS. Invention is credited to Mazen ALAMIR, Vincent DEBUSSCHERE, Lauric GARBUIO, Nouredine HADJ-SAID, Audrey MOULICHON, Mustapha Amine RAHMANI, Miao-Xin WANG.
Application Number | 20200091720 16/522118 |
Document ID | / |
Family ID | 65201504 |
Filed Date | 2020-03-19 |
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United States Patent
Application |
20200091720 |
Kind Code |
A1 |
MOULICHON; Audrey ; et
al. |
March 19, 2020 |
CONTROL METHOD OF A GENERATOR
Abstract
A method of controlling a generator including an inverter with
electronic switches which, controlled on the basis of instantaneous
cyclic ratios .alpha..sub.abc, enable the inverter to deliver to an
electrical distribution grid an electrical power P.sub.abc at an AC
voltage V.sub.abc, termed the source voltage, and an AC current
I.sub.abc, termed the source current, the voltage V.sub.abc and
current I.sub.abc having a frequency f.sub.abc, the inverter being
controlled by a control law that includes: a) an integration loop
to evaluate a difference .epsilon. between the current I.sub.abc
and a grid current I.sub.r actually required by the electrical
distribution grid; b) a correction loop which, as soon as the
difference .epsilon. is greater than a difference .epsilon.* termed
the reference difference, controls the adjustment by the source
current inverter of the instantaneous cyclic ratios .alpha..sub.abc
so as to reduce the difference .epsilon. to a value less than the
reference difference .epsilon.*.
Inventors: |
MOULICHON; Audrey;
(Grenoble, FR) ; ALAMIR; Mazen; (Saint Martin
D'Heres, FR) ; RAHMANI; Mustapha Amine; (Saint Martin
D'Heres, FR) ; GARBUIO; Lauric; (Saint Martin le
Vinoux, FR) ; DEBUSSCHERE; Vincent; (Grenoble,
FR) ; WANG; Miao-Xin; (Montbonnot Saint Martin,
FR) ; HADJ-SAID; Nouredine; (Grenoble, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schneider Electric Industries SAS |
Rueil Malmaison |
|
FR |
|
|
Assignee: |
Schneider Electric Industries
SAS
Rueil Malmaison
FR
|
Family ID: |
65201504 |
Appl. No.: |
16/522118 |
Filed: |
July 25, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 3/381 20130101;
H02J 3/50 20130101; H02J 2300/20 20200101; H02M 7/537 20130101;
H02J 3/48 20130101; H02M 7/44 20130101; H02J 3/388 20200101; H02M
1/42 20130101; H02J 3/38 20130101; H02J 3/382 20130101; H02J 3/46
20130101; H02J 2300/10 20200101; H02J 3/18 20130101 |
International
Class: |
H02J 3/18 20060101
H02J003/18; H02J 3/38 20060101 H02J003/38; H02M 1/42 20060101
H02M001/42; H02M 7/537 20060101 H02M007/537 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2018 |
FR |
18 58434 |
Claims
1. A method of controlling a generator comprising an inverter
provided with electronic switches which, controlled on the basis of
instantaneous cyclic ratios .alpha..sub.abc, enable said inverter
to deliver to an electrical distribution grid an electrical power
P.sub.abc at an AC voltage V.sub.abc, termed the source voltage,
and an AC current I.sub.abc, termed the source current, said
voltage V.sub.abc and current I.sub.abc having a frequency
f.sub.abc, the inverter being controlled by a control law that
comprises: a) an integration loop configured to evaluate a
difference .epsilon. between the source current I.sub.abc and a
current I.sub.r, termed the grid current, estimated by an
observation loop and actually required by the electrical
distribution grid; b) a correction loop which, as soon as the
difference .epsilon. is greater than a difference .epsilon.*,
termed the reference difference, controls the adjustment by the
inverter of the instantaneous cyclic ratios .alpha..sub.abc in such
a manner as to reduce the difference .epsilon. to a value less than
the reference difference .epsilon.*.
2. The method according to claim 1, wherein the grid current
I.sub.r is estimated on the basis of the source voltage V.sub.abc,
the source current I.sub.abc and the frequency f.sub.abc.
3. The method according to claim 1, wherein the step a) includes
measurement of the source voltage V.sub.abc, the source current
I.sub.abc, and the frequency f.sub.abc, and the source voltage
V.sub.abc, the source current I.sub.abc, and the frequency
f.sub.abc are measured at the level of terminals connecting the
inverter to the electrical distribution grid.
4. The method according to claim 1, wherein the observation loop
also estimates based on the source voltage V.sub.abc, the source
current I.sub.abc and the frequency f.sub.abc, a voltage V.sub.r,
termed the grid voltage, actually required on the electrical
distribution grid, the grid voltage V.sub.r and the grid current
I.sub.r being estimated on the basis of a model of the connection
of the inverter to the electrical grid.
5. The method according to claim 4, wherein the correction loop
determines, on the basis of the grid voltage V.sub.r and the
difference .DELTA..epsilon. between the difference s and the
reference difference .epsilon.*, a current and a voltage
respectively termed adjusted current I.sub.abcref and the adjusted
voltage V.sub.abcref that the inverter must actually deliver to the
electrical distribution grid.
6. The method according to claim 5, wherein the correction loop
estimates a first adjustment difference .epsilon..sub.x between the
adjusted current I.sub.abcref and the source current I.sub.abc and
between the adjusted voltage V.sub.abcref and the source voltage
V.sub.abc.
7. The method according to claim 5, wherein the correction loop
estimates a second adjustment difference .epsilon..sub.u between
the adjusted ratios .alpha..sub.ref and the instantaneous cyclic
ratios .alpha..sub.abc, the adjusted ratios .alpha..sub.ref being
the cyclic ratios enabling the inverter to deliver the adjusted
current I.sub.abcref and the adjusted voltage V.sub.abcref.
8. The method according to claim 6, wherein the correction loop
estimates, on the basis of the first adjustment difference
.epsilon..sub.x and the second adjustment difference
.epsilon..sub.u, the correction .DELTA..alpha..sub.ref to be made
to the instantaneous cyclic ratios .alpha..sub.abc for the inverter
to deliver the adjusted current I.sub.abcref.
9. The method according to claim 1, wherein the difference
.epsilon. is evaluated in successive time increments in such a
manner as to determine the evolution thereof.
10. The method according to claim 9, wherein the dynamic of
adjustment by the inverter of the source current I.sub.abc depends
on the evolution of the difference .epsilon..
11. The method according to any one of the preceding claim 1,
wherein the inverter forms with at least one source of renewable
energy, an accumulation system including a reserve of power and/or
of energy, and the control law, a virtual generator, the electrical
power P.sub.abc being an active and/or reactive power controlling
by statism, respectively, the frequency f and the RMS voltage
V.sub.rms of the source voltage V.sub.abc, the method comprising
control of the virtual generator by the control law so that it the
virtual generator executes an adjustment of the power P.sub.abc
delivered to the electrical distribution grid, said adjustment
being adapted to compensate a variation of the active/reactive
power consumed by the grid.
12. The method according to claim 11, wherein the control law is
adapted to confer on the virtual generator, via the inverter, the
possibility of forming the grid.
13. The method according to claim 11, wherein the control law is
adapted to connect the virtual generator in parallel with at least
one other power production source connected to the distribution
grid.
14. The method according to claim 11, wherein the accumulation
system applies a DC voltage V.sub.ref to first terminals of the
energy source so that the energy source delivers a power P.sub.sr,
said power P.sub.sr is liable to feature power fluctuations, the
accumulation system is controlled to compensate the
fluctuations.
15. A computer program comprising instructions which, when the
program is executed by a computer or a controlled card, lead to
execution of the method according to claim 1.
16. A generator comprising an inverter provided with electronic
switches which, controlled on the basis of instantaneous cyclic
ratios .alpha..sub.abc, enable said inverter to deliver to an
electrical distribution grid an electrical power P.sub.abc at an AC
voltage V.sub.abc, termed the source voltage, and an AC current
I.sub.abc, termed the source current, said voltage V.sub.abc and
current I.sub.abc having a frequency f.sub.abc, the inverter being
controlled by a control law that includes: a) an integration loop
intended to evaluate a difference .alpha. between the source
current I.sub.abc and a current I.sub.r, termed the grid current,
estimated by an observation loop and actually required by the
electrical distribution grid; b) a correction loop which, as soon
as the difference .epsilon. is greater than a difference .epsilon.*
termed the reference difference, controls the adjustment by the
inverter of the instantaneous cyclic ratios .alpha..sub.abc in such
a manner as to reduce the difference .epsilon. to a value less than
the reference difference .epsilon.*.
Description
TECHNICAL FIELD
[0001] The present invention concerns a method of controlling a
generator, and more particularly a generator including an
inverter.
[0002] The present invention concerns in particular a method of
controlling a generator intended to ensure stable operation of the
latter.
Prior Art
[0003] The virtual generator concept, highlighted in particular by
the introduction of microgrids, is known in the prior art and
described in the document [1] cited at the end of the
description.
[0004] A generator of this kind in particular includes a source of
electrical power, such as photovoltaic panels, and an inverter. The
source of electrical power generates a DC voltage and a DC current
intended to be converted by the inverter into an AC voltage and an
AC current before being injected into the electrical distribution
grid.
[0005] This virtual generator has a control law enabling said
generator to reduce (smooth) the effect of electrical power
fluctuations of the power source on the electrical distribution
grid.
[0006] Under some conditions a virtual generator of this kind may
nevertheless exhibit instabilities, in particular in the event of a
short circuit and in the event of a low current circulating in the
microgrid.
[0007] In order to alleviate this problem, impedances, termed
virtual impedances, have been considered in the control law in
order to guarantee the stability of the model governing it. To this
end, the person skilled in the art may consult the document [2]
cited at the end of the description.
[0008] However, the configuration of such impedances can be
complicated, and is above all dependent on the architecture of the
microgrid in which the virtual generator is installed.
[0009] Moreover, the use of virtual impedances imposes sampling the
current, in particular a reference current, at the output of the
inverter commensurately affecting the efficiency of the virtual
generator.
[0010] An object of the present invention is therefore to propose a
method of controlling a generator enabling stable operation of the
latter to be assured.
[0011] Another object of the present invention is to propose a
method of controlling a generator that is little or not at all
dependent on the generator concerned.
[0012] Another object of the present invention is to propose a
method of controlling a generator enabling stable operation of the
latter to be assured that is simpler to implement than the known
prior art methods.
SUMMARY OF THE INVENTION
[0013] The objects of the invention are at least in part achieved
by a method of controlling a generator including an inverter
provided with electronic switches which, controlled on the basis of
instantaneous cyclic ratios .alpha..sub.abc, enable said inverter
to deliver to an electrical distribution grid an electrical power
P.sub.abc at an AC voltage V.sub.abc, termed the source voltage,
and an AC current I.sub.abc, termed the source current, said
voltage V.sub.abc and current I.sub.abc having a frequency
f.sub.abc, the inverter being controlled by a control law that
includes:
[0014] a) an integration loop intended to evaluate a difference
.epsilon. between the source current I.sub.abc and a current
I.sub.r, termed the grid current, estimated by an observation loop
and actually required by the electrical distribution grid;
[0015] b) a correction loop which, as soon as the difference
.epsilon. is greater than a difference .epsilon.* termed the
reference difference, controls the adjustment by the inverter of
the instantaneous cyclic ratios .alpha..sub.abc in such a manner as
to reduce the difference .epsilon. to a value less than the
reference difference .epsilon.*.
[0016] According to one embodiment, the grid current I.sub.r is
estimated on the basis of the source voltage V.sub.abc, the source
current I.sub.abc and the frequency f.sub.abc.
[0017] According to one embodiment, the step a) includes
measurement of the source voltage V.sub.abc, the source current
I.sub.abc, and the frequency f.sub.abc, and the source voltage
V.sub.abc, the source current I.sub.abc, and the frequency
f.sub.abc are advantageously measured at the level of terminals
connecting the inverter to the electrical distribution grid.
[0018] According to one embodiment, the observation loop also
estimates on the basis of the source voltage V.sub.abc, the source
current I.sub.abc and the frequency f.sub.abca voltage V.sub.r,
termed the grid voltage, actually required on the electrical
distribution grid, the grid voltage V.sub.r and the grid current
I.sub.r being estimated on the basis of a model of the connection
of the inverter to the electrical distribution grid.
[0019] According to one embodiment, the correction loop determines,
on the basis of the grid voltage V.sub.r and the difference
.DELTA..epsilon. between the difference .epsilon. and the reference
difference .epsilon.*, a current and a voltage respectively termed
the adjusted current I.sub.abcref and the adjusted voltage
V.sub.abcref that the inverter must actually deliver to the
electrical distribution grid.
[0020] According to one embodiment, the correction loop estimates a
first adjustment difference .epsilon..sub.x between the adjusted
current I.sub.abcref and the source current I.sub.abc and between
the adjusted voltage V.sub.abcref and grid voltage V.sub.r.
[0021] It is understood that the first adjustment difference
includes at least two components respectively relating to the
difference between the adjusted current I.sub.abcref and the source
current I.sub.abc and the difference between the adjusted voltage
V.sub.abcref and the grid voltage V.sub.r.
[0022] According to one embodiment, the correction loop estimates a
second adjustment difference .epsilon..sub.u between the adjusted
ratios .alpha..sub.ref and the instantaneous cyclic ratios
.alpha..sub.abc, the adjusted ratios .alpha..sub.ref being the
cyclic ratios enabling the inverter to deliver the adjusted current
I.sub.abcref and the adjusted voltage V.sub.abcref
[0023] According to one embodiment, the correction loop estimates,
on the basis of the first adjustment difference .epsilon..sub.x and
the second adjustment difference .epsilon..sub.u, the correction
.DELTA..alpha..sub.ref to be made to the instantaneous cyclic
ratios .alpha..sub.abc for the inverter to deliver the adjusted
current I.sub.abcref.
[0024] According to one embodiment, the difference .epsilon. is
evaluated in successive time increments in such a manner as to
determine the evolution thereof.
[0025] According to one embodiment, the dynamic of adjustment by
the inverter of the source current I.sub.abc depends on the
evolution of the difference .epsilon..
[0026] According to one embodiment, the inverter forms with at
least one source of energy, advantageously of renewable energy, an
accumulation system including a reserve of power and/or of energy,
and the control law, a virtual generator, the electrical power
P.sub.abc being an active and/or reactive power controlling by
statism, respectively, the frequency f and the RMS voltage
V.sub.rms of the source voltage V.sub.abc, the method including
control of the virtual generator by the control law so that it
executes an adjustment of the power P.sub.abc delivered to the
electrical distribution grid, said adjustment being adapted to
compensate a variation of the active/reactive power consumed by the
grid.
[0027] According to one embodiment, the control law is adapted to
confer on the virtual generator, advantageously via the inverter,
the possibility of forming the grid.
[0028] According to one embodiment, the control law is adapted to
connect the virtual generator in parallel with at least one other
power source connected to the distribution grid.
[0029] According to one embodiment, the accumulation system applies
a DC voltage V.sub.ref to first terminals of the energy source so
that the energy source delivers a power P.sub.sr, said power
P.sub.sr is liable to feature power fluctuations, the accumulation
system is controlled to compensate the fluctuations.
[0030] The invention also concerns a computer program including
instructions which, when the program is executed by a computer or a
control card, lead to execution of the method according to the
present invention.
[0031] The invention also concerns a generator including an
inverter provided with electronic switches which, controlled on the
basis of instantaneous cyclic ratios .alpha..sub.abc, enable said
inverter to deliver to an electrical distribution grid an
electrical power P.sub.abc at an AC voltage V.sub.abc, termed the
source voltage, and an AC current I.sub.abc, termed the source
current, said voltage V.sub.abc and current I.sub.abc having a
frequency f.sub.abc, the inverter being controlled by a control law
that includes:
[0032] a) an integration loop intended to evaluate a difference
.epsilon. between the source current I.sub.abc and a current
I.sub.r, termed the grid current, estimated by an observation loop
and actually required by the electrical distribution grid;
[0033] b) a correction loop which, as soon as the difference
.epsilon. is greater than a difference .epsilon.* termed the
reference difference, controls the adjustment by the inverter of
the source current I.sub.abc in such a manner as to reduce the
difference .epsilon. to a value less than the reference difference
.epsilon.*.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] Other features and advantages will become apparent in the
following description of embodiments of the method according to the
invention of controlling a generator, given by way of nonlimiting
example with reference to the appended drawings, in which:
[0035] FIG. 1 is a diagrammatic representation of a known prior art
virtual generator described in the document [1] cited at the end of
the description, the generator shown including a source of
renewable energy;
[0036] FIG. 2 is a diagrammatic representation of the method
according to the present invention;
[0037] FIG. 3 is a representation of the frequency f of the current
and of the voltage as a function of the active power P delivered by
an electrical generator set, the frequency f being represented on
the vertical axis and the active power P on the horizontal
axis;
[0038] FIG. 4 is a representation of the RMS voltage V.sub.rms of
the voltage V as a function of the reactive power Q delivered by
the electrical generator set, the RMS voltage V.sub.rms being
represented on the vertical axis and the reactive power Q on the
horizontal axis;
[0039] FIG. 5 is a representation of an equivalent electrical
circuit diagram of the connection of the inverter to the electrical
distribution grid.
DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS
[0040] The present invention described in detail hereinafter
employs a method of controlling a generator including an inverter
delivering to an electrical distribution grid an electrical power
P.sub.abc.
[0041] In particular, the generator employs a control law enabling
adjustment of the current delivered to the distribution grid so
that there is an equilibrium between the power consumed and the
power supplied.
[0042] The invention will now be described in the context of a
virtual generator, and in particular in the context of the virtual
generator described in the document [1]. In this regard, the
content of the document [1] is hereby incorporated by
reference.
[0043] The invention, although described in the context of the
virtual generator, must not be limited to that aspect, however. In
particular, any generator generally including an inverter 4
intended to inject an AC current and an AC voltage into a grid
could be considered.
[0044] By virtual generator is meant a generator behaving like an
electrical generator set.
[0045] A virtual generator 1 according to the present invention
includes an inverter 4 that delivers to an electrical distribution
grid an active/reactive power P.sub.abc.
[0046] The active power P.sub.abc and the reactive power Q.sub.abc
are characterized by an AC voltage V.sub.abc, termed the source
voltage, and an AC current I.sub.abc, termed the source current,
both at a frequency f.sub.abc.
[0047] The source voltage V.sub.abc and the source current
I.sub.abc are respectively the result of conversion by the inverter
4 of a DC voltage V.sub.c and a DC current I.sub.c produced by an
energy source 2.
[0048] The energy source 2 may be a source of renewable energy, and
for example employ photovoltaic panels, wind power, water power,
thermodynamic machines.
[0049] The inverter 4 includes electronic switches which,
controlled on the basis of cyclic ratios termed instantaneous
cyclic ratios .alpha..sub.abc, impose said inverter 4 delivering
the source current I.sub.abc of frequency f.sub.abc.
[0050] The electronic switches may for example comprise insulated
gate bipolar transistors (IGBT).
[0051] The virtual generator 1 may also include a power and/or
energy accumulation system 3.
[0052] The virtual generator 1 according to the invention is
controlled by a control law that incorporates differential
equations enabling modelling of the functioning (behaviour) of the
electrical generator set. Thus the virtual generator 1 is
configured to emulate the behaviour of a synchronous generator, and
more particularly that of an electrical generator set. Configuring
the virtual generator 1 then includes determining the differential
equations governing the operation of the synchronous generator and
developing a computer program (or algorithm) based on said
differential equations. This is a configuration technique known to
the person skilled in the art and is described in the document
[1].
[0053] In this regard, and referring to FIG. 1 (FIG. 1a of the
document [1]), the control law may include various control blocks.
The latter includes in particular a block 100 denoted "virtual
generator".
[0054] It is understood that the control law is executed by
information technology means such as a computer, a processor, or
again a control card provided for example with a processor.
[0055] Via the block 100, the control law imposes delivery by the
inverter 4 of the source current I.sub.abc. The reference value of
the current I.sub.abc may be determined by the block 100 as a
function of the voltage V.sub.abc delivered by the inverter 4 and
measured at its output (V.sub.abcmes). The inverter 4 therefore
produces the current I.sub.abc from an electrical generator set
delivering a voltage V.sub.abc and satisfying the differential
equations modelling said electrical generator set.
[0056] The control law of the inverter 4 is also adapted, using
techniques known to the person skilled in the art, to confirm on
the virtual generator 1 the possibility of forming the grid (a
process known as "grid forming").
[0057] The virtual generator 1 can therefore on its own supply
electrical power to the microgrid just as an electrical generator
set would.
[0058] The control law is also adapted to enable the virtual
generator 1 to respond to load calls from the electrical
distribution grid.
[0059] A load call includes either connection or disconnection of a
load or a variation of the power consumed by said load on the
electrical distribution grid.
[0060] The control law, and more particularly the block 100, may
employ an observation loop 101, an integration loop 102 and a
correction loop 103.
[0061] The observation loop 101 is intended to determine a current
I.sub.r, termed the grid current, actually required by the
electrical distribution grid.
[0062] The grid current I.sub.r may be estimated on the basis of
the source voltage V.sub.abc and the source frequency
f.sub.abc.
[0063] In fact, as soon as a load is connected to or disconnected
from the electrical distribution grid a load call makes itself felt
directly at the level of the connection between the inverter 4 and
the electrical distribution grid and is reflected in a variation up
or down of the source current I.sub.abc and the source voltage
V.sub.abc.
[0064] These variations, and in particular the variation of the
source voltage V.sub.abc, make it possible to determine the grid
current I.sub.r by modelling the connection between the inverter 4
and the electrical distribution grid.
[0065] According to the same principle, the observation loop 101
also estimates on the basis of the source voltage V.sub.abc, the
source current I.sub.abc and the frequency f.sub.abc the voltage
V.sub.r, termed the grid voltage, actually required on the
electrical distribution grid.
[0066] This modelling, which relies on the characteristics of the
electrical distribution grid and on the inverter 4, is well known
to the person skilled in the art and is therefore not described in
detail in the present application.
[0067] This modelling in particular establishes equations for the
connection of the inverter 4 to the electrical distribution grid.
In this regard, FIG. 5 shows the equivalent electrical circuit
diagram of the connection between the inverter 4 and the electrical
distribution grid. The symbols appearing in FIG. 5 are defined in
the following table:
TABLE-US-00001 Notation V.sub.DC DC voltage of the inverter
V.sub.abc, V.sub.abc.sup.d and Respectively, single-wire voltage of
the inverter, V.sub.abc.sup.q and voltage of the inverter on the
axis dq and per unit, with V i = .alpha. V DC 2 ##EQU00001##
a.sub.d and a.sub.q Cyclic ratios of the inverter, respectively on
the axis dq and per unit V.sub.c, e.sup.d and e.sup.q Respectively,
single-wire filtered voltage, voltage filter on the axis dq, and
per unit V.sub.r, V.sub.r.sup.d and V.sub.r.sup.q Respectively,
single-wire grid voltage, and grid voltage on the axis dq and per
unit i.sub.abc, i.sub.abc.sup.d and i.sub.abc.sup.q Respectively,
single-wire inverter current, and inverter current on the axis dq
and per unit i.sub.r, i.sub.r.sup.d and i.sub.r.sup.q Respectively,
single-wire grid current, and grid current on the axis dq and per
unit L.sub.L and R.sub.L Respectively, impedance and resistance of
the inverter L.sub.r and R.sub.r Respectively, impedance and
resistance of the grid C.sub.f and R.sub.f Respectively,
capacitance and resistance of the filter
[0068] The observation loop is therefore able to measure the source
current I.sub.abc, the source voltage V.sub.abc and the frequency
f.sub.abc in order to detect a load call. In particular, the source
voltage V.sub.abc, the source current I.sub.abc and the frequency
f.sub.abc are measured at the level of terminals connecting the
inverter 4 to the electrical distribution grid.
[0069] The measurement may be executed at regular time intervals,
for example at a frequency of 6.66 kHz.
[0070] The integration loop 102 evaluates a difference .epsilon.
between the source current I.sub.abc and the grid current I.sub.r
estimated by the observation loop.
[0071] This difference .epsilon. can then be compared to a
difference .epsilon.* termed the reference difference. The result
of this comparison is a difference termed the integration
difference denoted .epsilon..sub.int.
[0072] The reference difference .epsilon.* may be, for example,
less than 10%, preferably less than 5%. In a particularly
advantageous manner, the reference difference .epsilon.* is
zero.
[0073] The integration difference .epsilon..sub.int may be
evaluated at regular time intervals, for example at a frequency of
20 kHz.
[0074] The integration loop 102 is also able to evaluate the
evolution of the integration difference .epsilon..sub.int. In
particular, the integration loop 102 is able to evaluate the
difference .epsilon..sub.int between two successive integration
differences .epsilon..sub.int.
[0075] The correction loop 103 is adapted to control adjustment by
the inverter 4 of the source current I.sub.abc. In particular, as
soon as the difference .epsilon. is greater than the reference
difference .epsilon.*, the correction loop 103 calculates the
cyclic ratios .alpha..sub.ref enabling the inverter 4 to reduce the
difference .epsilon. to a value less than the reference difference
.epsilon.*.
[0076] In particular, on the basis of the grid voltage V.sub.r and
the difference between the difference .epsilon. and the reference
difference .epsilon.* the correction loop 103 determines a current
I.sub.abcref and a voltage V.sub.abcref respectively termed the
adjusted current and the adjusted voltage that the inverter 4 must
actually deliver to the electrical distribution grid.
[0077] Determination of the adjusted current I.sub.abcref and of
the voltage V.sub.abcref is then followed by estimation by the
correction loop 103 of a difference .epsilon..sub.x, termed the
first adjustment, between said adjusted current I.sub.abcref and
the source current I.sub.abc and between the adjusted voltage
V.sub.abcref and the source voltage Vabc.
[0078] The correction loop is also able to evaluate a difference
.epsilon..sub.u termed the second reference difference of the
adjusted cyclic ratios .alpha..sub.ref and the instantaneous cyclic
ratios .alpha..sub.abc associated with the current I.sub.abc
actually delivered by the inverter 4.
[0079] On the basis of the first adjustment .epsilon..sub.x and the
second adjustment .epsilon..sub.u, the correction loop determines
the correction .DELTA..alpha..sub.ref to be made to the cyclic
ratios for the inverter 4 to deliver to the electrical distribution
grid the adjusted current I.sub.abcref. In a particularly
advantageous manner, the correction loop 103 includes a linear
quadratic regulator.
[0080] In a particularly advantageous manner, the virtual generator
1 uses control by statism at frequency f.sub.abc/active power
P.sub.abc. Control by statism at frequency f.sub.abc/active power
P.sub.abc is a characteristic of a synchronous generator, such as
an electrical generator set. An electrical generator set generally
includes a shaft driven in rotation by a diesel engine at a
frequency that corresponds to the frequency f of the current and of
the voltage produced by said set. The shaft frequency follows
control by statism at frequency f/active power P in accordance with
a law shown in FIG. 3. The control by statism at frequency f/active
power P enables the electrical generator set to adapt the frequency
f of the signal that it delivers as a function of the active
electrical power P that it supplies. This statism effect enables
parallel connection of different electrical generator sets that
will deliver to the grid a current and a voltage at the same
frequency f. In the context of the virtual generator 1 according to
the invention, the frequency f of the current and of the voltage
delivered by said virtual generator 1 depend on the specifications
of the microgrid (known as the grid code). For example, the
frequency f may be between 48 and 52 Hz inclusive, or again between
49.5 and 50.5 Hz, or between 58 and 62 Hz, or between 59.5 and 60.5
Hz.
[0081] Also in a particularly advantageous manner, the virtual
generator 1 also employs control by statism at RMS voltage
V.sub.rms/reactive power Q (V.sub.rms being the RMS voltage of the
source voltage V.sub.abs). Control by statism at RMS voltage
V.sub.rms/reactive power Q is a characteristic of a synchronous
generator such as an electrical generator set. An electrical
generator set generally includes a rotor driven in rotation inside
a stator and an automatic voltage regulator (AVR) operating on the
rotor windings of the rotor. The automatic voltage regulator
therefore applies to the rotor a voltage as a function of a voltage
of the electrical signal (and therefore the power) delivered by the
stator (by the electrical generator set) to the grid. The RMS
voltage V.sub.rms of the electrical signal delivered by the
electrical generator set follows control by statism at RMS voltage
V.sub.rms/reactive power Q in accordance with a law shown in FIG.
4. Control by statism at RMS voltage V.sub.rms/reactive power Q
enables the electrical generator set to adapt the RMS voltage
V.sub.rms of the voltage that it delivers as a function of the
reactive electrical power Q that it supplies.
[0082] The method of controlling the inverter as described
hereinabove is independent of the configuration of the grid or of
the installation concerned and has a simpler configuration relative
to the known prior art control methods.
REFERENCES
[0083] [1] EP3208907; [0084] [2] Rahmani et al., "Virtual
Synchronous Generators for microgrid stabilization: Modeling,
implementation and experimental validation on a microgrid
laboratory", IEEE 2017 Asian Conference on Energy, Power and
Transportation Electrification.
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